The present invention relates in general to driving tips for use in connection with pile driving rigs for forming cast-in-place caseless concrete piles. More particularly, the present invention relates to the construction and configuration of various tip members or foot members which are to be releasably assembled onto a hollow driving mandrel and driven into the ground to form a pile forming cavity or hole which is supplied with flowable concrete or fill material either concurrently with the driving operation or otherwise to form the cast-in-place caseless pile, the driving mandrel being withdrawn for reuse while the driving tip or foot member remains in the ground as the lower extremity of the pile.
One known procedure for forming caseless concrete piles in which the driving tips or foot members of the present invention may be advantageously used involves advancing into the soil a pile tip or driving member, achieved, for example, by the use of a hollow driving mandrel and conventional pile driving rig, and continuously providing an adequate supply of fluid or flowable concrete or similar fill material about and/or within the mandrel so that the concrete can flow or be directed into the ground cavity being formed by the driving tip and mandrel. In one preferred embodiment, the mandrel is an elongated tubular hollow driving member of cylindrical configuration with a large central bore extending from end to end and having a plurality of holes or slots distributed about the tube wall of the mandrel to permit significant flow of the concrete or fill material between the space within the hollow bore of the mandrel and the space immediately outwardly of the exterior mandrel surface. Usually, some type of receptacle or hopper device, usually called a fill hopper, having downwardly inclined converging wall portion converging to a central lower discharge opening is placed on the ground at the pile site and the mandrel, releasably coupled with the driving tip or foot member, extends downwardly through the upwardly opening receptacle portion of the hopper and the lower discharge opening. As the driving tip or foot member is driven into the ground by the energy supplied to the mandrel, thereby producing a pile forming cavity or hole in the ground immediately below and communicating with the lower discharge opening of the hopper, the fill material flows by gravity into the annular space immediately surrounding the mandrel between the mandrel surface and the perimeter of the discharge opening and flows also through the holes or slots in the tube wall of the mandrel into the central bore of the mandrel and downwardly to maintain the space within the pile forming cavity not occupied by the mandrel and boot completely filled with the flowable concrete or fill material. When the driving tip has been driven to the desired depth to produce a pile forming hole or cavity of appropriate axial height, the mandrel is then withdrawn upwardly permitting flowable concrete to fill the space previously occupied by the tube walls of the mandrel and such additional concrete flows from the hopper into the upper portions of the pile cavity to properly top off the concrete pile. The mandrel and fill hopper devices are then moved to the next pile site to repeat the procedure and form another cast-in-place concrete pile.
In practicing the method of forming caseless cast-in-place concrete piles by driving a tip or driving foot member releasably coupled on the bottom of a driving mandrel extending vertically downwardly through a fill hopper, and concurrently supplying concrete in flowable condition into the cavity or pile-forming fold as it is being formed, a number of problems are encountered in regard to the configuration, design, and structural nature of the driving tip member. When the driving tip member is in the general configuration of a boot assembled onto the lower end of the mandrel, wherein the boot has a bottom plate of generally circular configuration and a cylindrical sleeve extending upwardly from the bottom or leading end plate, difficulties are encountered in centering the boot on the mandrel and maintaining it in proper alignment. Also, when working in difficult conditions, particularly where large amounts of water are present, difficulty has been encountered in centering the driving tip over the exact pile location. Furthermore, in forming piles with the herein described method, it is sometimes found desirable to permit fill material to flow from the inside of the mandrel to the outside of the pile cavity externally of the outer surface of the driving boot or tip. For example, it may be desirable to continuously supply fill material from the region within and surrounded by the drive boot to the region immediately outwardly surrounding the outer surface of the sleeve or cylindrical portion of the boot to line the walls of the cavity being formed in the ground between the boot and the cavity wall with the fill material.
Another object of the present invention, therefore, is the provision of a driving boot construction for use in the hereinabove described pile-forming method, wherein the boot is furnished with surface portions which engage sides of the mandrel at a plurality of circumferentially spaced locations extending over a sufficient axial extent of the mandrel to maintain the boot substantially centered in coaxial relation on the mandril.
Yet another object of the present invention is the provision of a driving boot or tip construction for use in practicing the above-described pile-forming method, wherein a downwardly projecting elongated spike is formed on the underside of the leading end plate portion of the boot or tip to enter the soil and locate the plate portion of the boot at the precise pile location preliminary to and during the initial stages of driving of the boot to form the pile-forming hole.
Yet another object of the present invention is the provision of a driving boot construction for use in practicing the above-described pile-forming method, wherein perforations are provided in the sleeve or cylindrical portion of the boot to permit fill material flow between the zone surrounded by the sleeve portion of the boot and the region immediately outwardly of the external sleeve surface.
Yet another object of the present invention is the provision of a novel design for the driving tip member for use in forming piles by the above-descrived method with a driving mandrel, wherein economies in material and cost of the driving member are achieved by use of a generally circular driving plate having vertically extending locating elements, such as vertically extending rods secured to the plate, or U-shaped bar members assembled through apertures in the plate, or other locator formations adapted to enter the hollow bore portion of the hollow driving mandrel and releasably locate and center the plate-like driving tip member in proper relation to the driving mandrel.
Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings illustrating preferred embodiments of the invention.